Electronic timepieces

ABSTRACT

An electronic timepiece such as a wrist watch of the type employing all solid state components including an electronic or a liquid crystal output display for indicating time, utilizes a high efficiency up-converter to enable a small physical and low voltage battery to provide energy for the entire electronic watch assembly by applying said battery voltage to an inductor which conducts current under control of a switching circuit. The control of current through the inductor at specified intervals causes a high voltage pulse train to be developed which is then rectified to provide a higher DC voltage for providing operating potential for the entire electronic assembly of the timepiece. The stability of the voltage output can be enhanced by means of a feedback regulator.

United States Patent l l Luce et al.

[ Oct. 22, 1974 I I ELECTRONIC TIMEPIECES Primary Examiner-Edith Simmons.iackmon [75] Inventors: Nunzio A. Luce, Trenton; George A. AttorneyAgent or Frm JoeI Spwak Graham, Mercervillc Township, Mercer County,both of NJ. [57] ABSTRACT [73] Assignee: Optel Corporation, Township ofAn electronic timepiece such as a wrist watch of the South Brunswick,N]. type employing all solid state components including an [22] Filed,June 6 1973 electronic or a liquid crystal output display for indicatingtime, utilizes a high efficiency up-converter to en- [21] Appl. No.:362,176 able a small physical and low voltage battery to provide energyfor the entire electronic watch assembly [52] U S Cl 58/50 R S8/23 BA byapplying said battery voltage to an inductor which ['51] 19/30 6 3/00conducts current under control of a switching circuit. [58] Fie'ld R 23A BA 50 R The control of current through the inductor at specifledIntervals causes a high voltage pulse train to be [56] References Citeddeveloped which is then rectified to provide a higher DC voltage forproviding operating potential for the UNITED STATES PATENTS entireelectronic assembly of the timepiece. The sta- 3668.86 6/1 72 Dicrshocka 3 BA bility of the voltage output can be enhanced by means 37I588I 2I973 Girurd .I 58/23 R I 3,750,383 8/1973 Kakizawa 58/23 BA of afeedback regulator.

10 Claims, 2 Drawing Figures /5 ll-4B} RECTIFIER Egg D 7 [0 22 11 a 7 24LOGIC 33 PP MODULE SWITCHING 23 CIRCUIT CONTROL L CIRCUIT I6) I I rDRIVER I V CIRCUIT 3/ LIQLIID I CRYSTAL DIVIDERS DISPLAY r/ OSCILLATOR TELECTRONIC TIMEPIECES BACKGROUND OF INVENTION This invention relates toa power supply for an electronic wrist watch or timepiece and moreparticularly to a high efficiency up-converter circuit for use in such adevice.

The digital electronic wrist watch is a new development made possible byrecent technological advances. The movements of mechanical timepieces,though steadily improved and miniaturized over the centuries, still havethe disadvantage of wear of moving parts associated therewith. Thisdisadvantage is eliminated in an all electronic wrist watch with nomoving parts other than possibly a mechanical time setting switch usedonly when changing time zones or replacing the power supply of the watchsince other resetting will generally be unnecessary.

The main components of an electronic liquid crystal watch are a liquidcrystal display cell, a power supply, typically a 1.5 volt miniaturizedbattery as is presently commercially available, a crystal oscillator fortimekeeping, divider circuits for dividing the primary output frequencyof the crystal oscillator, counter, decoder and driver circuits foraccumulating the minutes and hours and driving the liquid display celland an upconverter for transforming the 1.5 volts supplied by the powersupply to, typically about volts required for the counter, decoder anddriver circuits and the liquid crystal display.

The advent of digital electronic wrist watches such as the liquidcrystal watch offers improvements in accuracy, reliability and ease ofreading time as compared with commonly available wrist watches. Itsunavailability heretofore is due to the strigent demands imposed uponcombining a liquid crystal display and the required electronics into asingle small package, available at reasonably low cost, and utilizinghigh efficiency electronics which do not require excessive power. In

order to achieve this it is important that the power requirements andsize of each part of the electronics be minimized. Available 1.5 voltcompact batteries can supply 30 u-watts of power continuously for oneyear. For practical considerations therefore, the power dissipation ofthe electronics and the liquid crystal display should be less than 30u-watts. Since a typical display cell has a power dissipation of about15 u-watts per year with continuous use, the total power dissipation ofthe electronics should not exceed 15 u-watts per year with continuoususe.

BRIEF DESCRIPTION OF PREFERRED EMBODIMENT In an electronic wrist watchcomprising in combination, a liquid crystal display cell, a low voltagepower supply, a frequency source, timekeeping and driver circuits and avoltage up-converter network for increasing the low voltage obtainedfrom the power supply to a higher voltage for operation of the liquidcrystal display cell, the improvement comprising a voltage upconverterincluding a relatively high Q inductor for storing energy in a magneticfield under the control of a switching circuit, operative according to asignal derived from said frequency source to thus convert said lowvoltage to a high voltage during one of two modes of said switchingcircuit.

BRIEF DESCRIPTION OF FIGURES FIG. 1 is a block diagram of an electronictimepiece employing a liquid crystal display and an up-converter circuitaccording to this invention.

FIG. 2 is a diagram indicating an embodiment of the control circuit andswitching circuit portions of FIG. 1.

DETAILED DESCRIPTION OF FIGURES Referring to FIG. 1 there is shown ablock diagram of an electronic timepiece employing a liquid crystaldisplay.

conventionally, such timepieces employ a battery 10 which, for example,is a low voltage (1.5 volts) compact device such as those found inhearing aids, watches and so on.

The output of battery 10 may be used directly in many watches ortimepieces to drive, for example, a tuning fork bias assembly or acrystal oscillator module or the voltage output of the battery may firstbe increased by means of an up-converter of some sort before drivingvarious portions of the timepiece.

In any event, the electronic timepiece further includes a timingoscillator 1 1. Oscillator 11 may be crystal controlled and is arelatively stable device. Stability is necessary to assure that the timekeeping functions remain accurate for long durations. The oscillator 11has its output coupled to a plurality of dividers 12. The function ofthe dividers 12 are to develop lower frequency signals from the stableoscillator signal and to use these signals to develop time keepingindicia.

Thus, the oscillator signal may be at a stable frequency of 32,768HZ.The dividers 12 function to divide this frequency to provide, forexample, a signal capable of manifesting pulses a minute analogous toseconds and count from this signal to develop minutes, hours, days andso on.

One skilled in the art will recognize the need for dividers and so on.

The divider module 12 may have a single output or multiple outputs shownas a single lead 14 which is coupled to counter/decoder and logic module15.

Primarily, the function of the counter/decoder and logic module circuits15 is to respond to the accurate divided oscillator signal to accumulatesignals indicative of seconds, minutes and hours.

Thus, module 15 includes counters which may be integrated circuitconfigurations, which counters are controlled according to the wellknown principles of time keeping.

The module 15 is coupled to a driver circuit module 16 Driver circuit 16may, for example, include a series of amplifiers as MOSFET or integratedcircuit devices for amplifying signals from the counters and associateddecoding circuits and applying these signals to a suitable liquidcrystal display as 17.

The liquid crystal display 17 is preferably driven by a bi-directionalcurrent as is evidenced by a co-pending application entitled LiquidCrystal Driving and Switching Apparatus.

This application has issued as US. Pat. No. 3,744,049 and assigned tothe assignee herein.

The liquid crystal display 17 is typically a multicharacter segmentednumeric digit display cell having at least four characters. Basically,the liquid crystal cell or display 17 is well known in the art andcomprises a hermetically sealed package consisting of a liquid crystalcomposition between two electrodes, one electrode is a common electrodefor all display characters and one electrode being segmented. Segmenteddisplays are extensively employed for all sorts of display media and arenot considered part of this invention, although the drive considerationsfor a liquid crystal display afford to determine certain necessaryfeatures in regard to the operation of the power supply.

Namely, the liquid crystal display 17 typically requires about volts toachieve good contrast and brightness but may be operable at lower orhigher voltages, e.g. 4-40 V. The power supply for the liquid crystaldisplay can be a 15 volt battery, however, suchbatteries are not compactor if so are extremely expensive.

Hence, one must use as small a battery as possible to implementphysicial and operating requirements. A battery in a digital watchshould have enough energy storage to operate a watch for about one yearand be small in size. Currently available batteries offer outputvoltages of 1.3 to 1.5 volts with capacities of 165 to 250milliamp-hour. A single compact l.5 volt battery can supply about 30microwatts of power continuously for one year. By using a liquid crystaldisplay 17 and low power semiconductor circuitry, a single 1.5 voltbattery will meet the power requirements. However, the voltage of 1.5has to be increased by at least three to 10 times to operate the typicalavailable display with low power circuits, reliability and with goodbrightness and contrast.

The 1.5 volt battery 10 therefore supplies power to an up-convertercircuit which is an inductive charging circuit operating at highefficiency. Accordingly, battery 10 is coupled via an inductor 20 to arectifier or diode circuit 21.

An optional capacitor 22 is shown coupled between the connection ofbattery 10 to inductor 20 and serves to linearize battery voltage overprolonged periods or during large temperature variations which wouldserve to affect the internal impedance of the battery 10. It also helpsto supply the higher current through the inductor 20 during the inductorcharging interval.

The inductor 20 has a relatively high Q and is selected of a valuedepending upon the described power and the switching rate.

Shown coupled to the connection between the inductor 20 and therectifier 21 is a switching circuit 24. Circuit 24 may comprise asuitable transistor, junction FET or other controllable switchingdevice. It is wellknown in the art that transistors and FETs, forexample, are three terminal devices. The terminals of these devices maybe termed the common electrode, output electrode, and control electrode.The switching circuit 24 serves to present a low impedance during afirst state and a high impedance during a second state. Thus during thefirst state, the output terminal of inductor 20 is relatively grounded;and during the second state it is opened circuited or at a largeimpedance.

The switching circuit 24 operates between the first and second statesunder control of the control circuit 23, which circuit is responsive toa signal derived from the previously described divider module 12associated with the time keeping crystal oscillator source 11. Theoutput of the control circuit is connected to the control electrode ofthe switching means 24. This can clearly be seen with referenceto FIG.2, wherein the switching circuit is shown to be a transistor, the baseof which is connected to the output of the control circuit 23, thecollector connected between the conductor 20 and the rectifier 21 andthe emitter being common to ground.

For example, as indicated with a crystal oscillator 11, selected tooperate at 32.768KHZ, the dividers 12 may be a nine stage, ripple carrybinary counter. The outputs of the divider circuit may be at 256HZ and64HZ. The 256HZ signal would be applied to the control circuit 23 tocontrol the switching circuit 24. Therefore, the rate of operation ofthe switching circuit 24 may be as high as 256HZ, thus permitting asmall physical capacitor 29 to be used at the output of the rectifier21.

The switching circuit 24, if a transistor, would be selected to have ahigh beta and a low saturation voltage to assure efficiency.

Besides capacitor 29 coupled to the output of the rectifier 21, there isa zener diode 30. The zener 30 serves to regulate the output of thesupply at l5 volts. The zener 30 may also be in series with a currentsensing resistor 31. The junction between resistor 31 and zener 30 iscoupled to the control circuit and will serve as a feedback control toaid in stabilizing the operation over varying circuit conditions andpower requirements 33 coupling the control circuit module 23 to therectifier 21.

As will be explained, rectifier 21 may be a synchronous rectifier andhence operate under control of the same control circuit 23 whichoperates the switch 24.

Synchronous control of the rectifier further increases efficiency of theunit but is not absolutely essential to operation.

OPERATION OF UP-CONVERTER The inductor 20, as indicated, is of arelatively high Q in order to minimize loss and increase efficiency.

As is well known, the current flowing through an inductor cannot changeinstantaneously. If one attempts to stop current flow in an inductor, alarge voltage spike will be developed. The amplitude and duration ofthis spike or transient is a function of the magnitude of the inductorand the magnitude and rate at which the current is varied.

Basically, one can say that the larger the current and the faster thetime required to stop the flow through an inductor, the larger thevoltage transient produced as:

wherein V is voltage, L is inductance, i is current and t is time.

The equation being well known and well understood.

Hence, the switching circuit 24 under control of the control circuit 23alternatively attempts to stop current flow and permit current flowthrough the inductor depending upon it being switched between the abovedescribed first and second states.

The rate of switching between first and second states is 256HZ, but canbe higher or lower if desired (100 to 1,000HZ). The pulses obtained fromcontrol circuit are relatively narrow and may be, for example, 15microseconds wide at a repetition rate of 256HZ.

Hence, during the first state, the switch 24 is on and therefore currentfrom battery 10 flows through inductor and switch 24 to ground. lnductor22 stores energy due to current flow creating a magnetic field. Theamount of energy stored is, of course, dependent upon the width of thepulse which caused switch 24 to saturate or operate in the first stateand, of course, the magnitude of the inductor 20 is also important.Therefore, by controlling the pulse width, one can control the energyprovided.

As soon as switch 24 is turned off or to the second state, the currentthrough the inductor has to change as the impedance to ground changes.As indicated, this change is accomplished by a voltage pulse whichtransfers the energy stored in the inductor 20 via the recitifier 21.Rectifier 21 produces DC from the large amplitude voltage pulse train.The rectified DC is filtered and stored across capacitor 29.

The output power is desireably controlled by means of varying the pulserepetition rate by feedback from the output zener diode to the controlcircuit 23 (Line 50). Essentially, the pulse repetition variation isused to control the output power. The output waveform consists of verynarrow spikes having a repetition rate determined by the repetition rateof the pulse train from the dividers 12. This pulse train is modified bythe control circuit such that the average power available is controlledby monitoring the output rectified voltage and varying the repetitionrate according to the power required by the load. Therefore, as morepower is required, the repetition rate would be decreased or thefrequency would be increased. If less power is required, the oppositewould be true. While pulse repetition rate is a preferred way of varyingpower, it is also noted that one could vary the pulse width whichessentially would also serve to determine the output power. Pulse widthvariation could be accomplished without varying the pulse repeitionrate.

If the rectifier 21 were under control of the control circuit improvedoperation would be provided. For example, when switch 24 is on, therectifier 21 would be off and hence all current would flow throughinductor 20 and switch 24 to therefore store the most energy possible asthe shunt path through an ordinary rectifier, due to leakage and so on,is relatively reduced. The same pulse or signal that turns the switch 24off now turns the rectifier 21 on, therefore, transferring maximumenergy to capacitor 29.

Briefly, the control circuit 23 can be of the type to provide a variablewidth pulse for regulation and as such can be a monostable multivibratorwhose pulse width could be varied as a function of the current flow viaresistor 31. Therefore, as the load (counter/decoder 15, driver andliquid crystal display) power requirements increase, the current through31 decreases. This decrease causes the control circuit to keep switch 24in the on state longer thus storing more energy in inductor 20, thusproviding more power when needed.

There are numerous configuration which can be used for the dividers 12and control circuit 23 which are known in the art. As such, they utilizemulitvibrators, gates and so on.

In any event, the advantages of the above described up-converter beingin utilizing small physical elements, under control of a clock circuitwhich signal is freely available in a timepiece because of time keepingfunctions. Thus, one can use a small voltage, compact battery and stilldevelop large voltage for good operation of a liquid crystal display.

We claim:

1. In an electronic timepiece of the type employing a relatively stableoscillator and associated frequency dividers for providing at outputsthereof respective signals of frequency rates necessary for time keepingoperations, said timepiece including a low voltage supply and a liquidcrystal display adapted for efficient operation at a given bias level inexcess of said low voltage supply, the combination therewith ofapparatus for converting said low voltage supply to said given biaslevel, comprising:

a. an inductor having a relatively high quality factor, said inductorhaving a first terminal coupled to a terminal of said low voltage supplyand a second output terminal,

b. switching means, having an output electrode, a common electrode and acontrol electrode, said switch ing means capable of being in a firststate indicative of a low impedence between said output and commonelectrodes, and in second state indicative of a high impedance betweenoutput and common electrodes, said states selected according to themagnitude of a control signal applied to said control electrode, saidoutput electrode of said switching means coupled to said second outputterminal of said inductor,

0. control means having an input responsive to one of said signals atone of said frequency rates provided by said dividers and an outputcoupled to said control electrode of said switching means forselectively causing said inductor to conduct current via said lowvoltage supply through said switch in said first state, and

d. utilization means coupled to said second output terminal of saidinductor and responsive to said second state to develop any energypreviously stored in said inductor during said first state into saidgiven bias level necessary to operate said liquid crystal efficiently.

2. The apparatus according to claim 1 wherein said one frequency rate atwhich said control means is responsive is in excess of lOOHZ.

3. The apparatus according to claim 1 wherein said switching meansinclude a transistor device having a low saturation voltage between anoutput collector electrode and a common emitter electrode; saidtransistor having a base control electrode, said collector electrodebeing coupled to said second output terminal of said inductor.

4. The apparatus according to claim 1 wherein said utilization meansinclude a zener diode having a first and second electrode, said firstelectrode coupled to said second output terminal of said inductor andsaid second electrode coupled to a point of reference potential, saidzener as coupled operative to conduct current to cause regulation ofsaid bias level.

5. The apparatus according to claim 4 further including a filtercapacitor in shunt with said zener diode.

6. The apparatus according to claim 1 wherein said low voltage supply isbetween 1 and 2 volts.

7. The apparatus according to claim 6 wherein said given bias level isbetween 4 to 20 volts.

8. The apparatus according to claim 1 further comprising:

a. means coupled to said utilization means and operative to monitor saidbias level to provide an indicator signal when said level varies beyonda given amount, and

b. feedback means coupled to said control means and responsive to saidindicator signal to vary the duration of said first state according tosaid indicator signal.

9. The apparatus according to claim 1 wherein said ing said secondstate.

10. The apparatus according to claim 9 further comprising:

a. synchronizing means coupled between said rectiutilization meansinclude arectifier havingafirst termifier and said control means andresponsive to one of nal coupled to said second output terminal of saidinductor and a second terminal coupled to said liquid crystal displayfor applying energy to said display dursaid selected states for biasingrectifier into conduction during said one selected state.

1. In an electronic timepiece of the type employing a relatively stableoscillator and associated frequency dividers for providing at outputsthereof respective signals of frequency rates necessary for time keepingoperations, said timepiece including a low voltage supply and a liquidcrystal display adapted for efficient operation at a given bias level inexcess of said low voltage supply, the combination therewith ofapparatus for converting said low voltage supply to said given biaslevel, comprising: a. an inductor having a relatively high qualityfactor, said inductor having a first terminal coupled to a terminal ofsaid low voltage supply and a second output terminal, b. switchingmeans, having an output electrode, a common electrode and a controlelectrode, said switching means capable of being in a first stateindicative of a low impedence between said output and common electrodes,and in second state indicative of a high impedance between output andcommon electrodes, said states selected according to the magnitude of acontrol signal applied to said control electrode, said output electrodeof said switching means coupled to said second output terminal of saidinductor, c. control means having an input responsive to one of saidsignals at one of said frequency rates provided by said dividers and anoutput coupled to said control electrode of said switching means forselectively causing said inductor to conduct current via said lowvoltage supply through said switch in said first state, and d.utilization means coupled to said second output terminal of saidinductor and responsive to said second state to develop any energypreviously stored in said inductor during said first state into saidgiven bias level necessary to operate said liquid crystal efficiently.2. The apparatus according to claim 1 wherein said one frequency rate atwhich said control means is responsive is in excess of 100HZ.
 3. Theapparatus according to claim 1 wherein said switching means inClude atransistor device having a low saturation voltage between an outputcollector electrode and a common emitter electrode; said transistorhaving a base control electrode, said collector electrode being coupledto said second output terminal of said inductor.
 4. The apparatusaccording to claim 1 wherein said utilization means include a zenerdiode having a first and second electrode, said first electrode coupledto said second output terminal of said inductor and said secondelectrode coupled to a point of reference potential, said zener ascoupled operative to conduct current to cause regulation of said biaslevel.
 5. The apparatus according to claim 4 further including a filtercapacitor in shunt with said zener diode.
 6. The apparatus according toclaim 1 wherein said low voltage supply is between 1 and 2 volts.
 7. Theapparatus according to claim 6 wherein said given bias level is between4 to 20 volts.
 8. The apparatus according to claim 1 further comprising:a. means coupled to said utilization means and operative to monitor saidbias level to provide an indicator signal when said level varies beyonda given amount, and b. feedback means coupled to said control means andresponsive to said indicator signal to vary the duration of said firststate according to said indicator signal.
 9. The apparatus according toclaim 1 wherein said utilization means include a rectifier having afirst terminal coupled to said second output terminal of said inductorand a second terminal coupled to said liquid crystal display forapplying energy to said display during said second state.
 10. Theapparatus according to claim 9 further comprising: a. synchronizingmeans coupled between said rectifier and said control means andresponsive to one of said selected states for biasing rectifier intoconduction during said one selected state.